1530 Part IX / Diseases of the Nervous System
Figure 62–6 Strikingly beautiful art work by George
Widener.George is a highly accomplished and much-admired
outsider artist. In the attention to detail, this drawing resembles
the drawings of other autistic savant artists. The intricate topo-
graphical detail of a symmetrically arranged city, with rivers,
bridges, and tall buildings, is combined with minutely executed
and seemingly abstruse calendar sequences. Mastery of the
calendar and the ability to name the day of the week for any
given date has often been described for autistic savants. The
viewer of this drawing can partake in an otherwise very private
world of space and time, numbers, and patterns. (Reproduced,
with permission, from the Henry Boxer Gallery, London.)
the time as comprising fundamental impairments in
each of three categories: social communication, lan-
guage development, and restricted interests or repeti-
tive behaviors. In contrast, dizygotic twins show 10%
to 30% concordance—again with the lower number
estimating concordance for the diagnosis of isolated
autism, while the larger number encompasses any of
three diagnoses on the autism spectrum.
This difference between the rates at which
monozygotic and dizygotic twins share an ASD phe-
notype is attributed to differences in the amount
of shared genetic material between the two types
of twin pairs. Monozygotic siblings share all their
DNA, whereas dizygotic twins share as much DNA
as any sibling pair. In addition to these types of data,
it has long been observed that ASD runs in fami-
lies: Current estimates are that if parents have one
child with ASD, the risk that a second child will be
affected increases approximately 5- to 10-fold over
the population base rate.
The most generous estimates of genetic contribu-
tion do not explain all risk for ASD in the population.
Some contribution from the environment is a certainty.
However, given the well-known public debate on the
issue of whether immunization is a factor in ASD, it
is important to note that there is no credible evidence
that the increase in ASD prevalence is due to immu-
nizations. The initial study that raised the issue of the
contribution of the trivalent measles-mumps-rubella
(MMR) vaccine has been retracted and thoroughly
repudiated by the editors of the journal in which the
article appeared, as well as by 10 of 12 of the original
authors. A wide range of subsequent investigations,
both of the MMR vaccine and of vaccines with the
mercury-containing preservative thimerosal, has found
no evidence for association with ASD risk.
The counter argument that certain rare individu-
als may be predisposed to a vulnerability to vaccines
leading to ASD is nonfalsifiable. However, three lines of
evidence suggest that such a contribution, if present, is
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